Reflex klystron oscillator



Nov. 10, 1953' H H GW 2,659,025

REFLEX KLYSTRON OSCILLATOR Filed March 29, 1946 .n o N /i Q L S I Q";

INVENTOR WILLIAM H. HU GG|NS ;e/ :MM 9

ATTORNEY- Patented Nov. 10, 1953 :2 ,1

)KUNITED s v v 7 IQR r't x x irsrnow'oscnmroit" i if f c :Willlam H. Huggins; Cambridge, Massg assiz'nor to.the ,United States of Americaas represented or. bythe SecretarypfWar .1. i 1 AppIicatlonlYIarchZS),1916;jserialNo.,d57,952 2 claims. (61. 31545) This-invention relates generally to aradio fre- {cavity 'will becoine' resonant at a fundamental wquency oscillatonand, more'particularlygto a --frequency 'and-produce ahighfrequency alterrefiex -klystron harmonic oscillator. natin'g voltage variation between grids l2 and :Ina reflex, velocity-modulated klystron,-a cavity resonator is used as the resonant element HR- The alternating voltage variation velocity modulates the-stream of electrons -to form which determines the frequency of oscillation. bunches of electrons. Thebunchesof electrons Power at the fundamental-frequency'of oscillaare stopped by virtue oft he strong retarding tionistaken from the cavity by means of a coufield-theirdirection -reversed-,= and they -are pling loop and coaxial line. An object of the sent backthroughthe cavity grids Someofthe present invention is to provide a cavity which 10 energy imparted to the electrons during the will be resonant or antiresonant at the fundabunching'process is then given to the cavity and mental frequency of oscillation and simuloscillations within the cavity aresustained'. taneously resonant or antiresonant at a har- -"-=Cavity-20 includes'an-outer-conductor 2| conmonic of theifundamental frequency and allow centrically spacedabout a center'sconductor 22. power at the harmonic frequency to be extracted Center conductor 22' is held'in place by means i from the cavity. The cavity is to be such that of a supporting disc23 attached to its outer end the kylstron will operate satisfactorily over a and also to 'theoutside conductor.Outer confairly wide'range .of frequencies; It is intended ductor 2| is closed-at theopposite endwbyia,- that the loading afiorded by the extraction of suitable metallic disc 123 which forms one end the power at the harmonic frequency will not 0f the cavity;

qafiectjthe amplitude of oscillation at the funda- Disc. I23 contains a hole 24 dire Y- hl 1menta1 frequency. the inside end'of center'conductor '22.--- Cavity Other objects, features and advantages of this id Il -is mounted hole I24 such a manner invention will suggest themselves to those skilled as to! afford 616011110311 continulty w d in the art and will become apparent from the 25 a d Supporting disc. C t r d. l sis mounted following description of the invention,.taken in across the inner endof centerconductor 22 so:as

. which:

connection with the accompanying drawings; i toaiford. electrical continuity ,:between ,the;.two.

i i i The outer end of center conductor 22 projects Fig. 1- is a cross-sectional view of a reflex through a hole in .disc23 to the outside. The klystron, harmonic oscillator embodying the d of th v y j nt, 'disc I23 will hereprinciples f thi i ti d J inafter be referred to as the inner e'nd of. the Fig. 2 is a cavity characteristic diagram which .cavitywill be used in explaining the operation of -the I The outer. endefeevitv i efietivelv e i o t of i 1, .circuited for direct current (D.-C,) potentialby .In Fig. 1 cavity20 is used as the resonant iemeans of w sl ann a pluneers, 2,4. -a d mentz of the klystron; The cavity structure will 3 ti w n nte to be described. more, fully laten indirectly and outer conductor 2|. Annular plunger 24 heated cathode fu cti as a source of Lmay include a cylindricalconductor 36 surround- -trons, which are accelerated toward the. cavity 9 Conductor 22, end plates 31, and slid- {grids n and 3 byvirtue of a suitable positive mg friction contacts 38;wh1ch bear on the ml tential from a source designated herein?" as 'Zside of Outer d -QF 3 Annular P 8 t |4 connected between gridand t b 25 contains sliding friction contacts 39 bearing .A control grid l5 which is placed between-the 01i annularplnnserfl. andslidingfrictioncgncathode and the cavity grids controls the number tacts bearlng the Outslde of mne'r 'c'on- 10f electrons that pass through ty. ductor 22. The relative lengths of the two "positive potential, less than that applied to the Plungers l h h p u ngertl is free to slide ctivity. is applied tofthe control grid-from'a suitover a p edete min distance si Peter 54 able source designated herein as battery t6. "'conductor' a d fill-Inger 5 free to Slide/over the strong retardingfield of the reflector anode Afterleaving the cavity grids,the electronsenter a pr d t rmined lengthen plunger 2d. The position of both plungers 24 and 25 may be ad- The potential of the reflector anode is mainjusted .by Suitable means suchiaslrods 25. and trained negative with respect to the cathode by a r 2 I. respectively, attached thereto and projecting suitable source of potential connected therebethrough holes in disc 23 to the outside...

tween and designated herein as battery 18'. --'I he 55- The inner conductor ofcoaxial line 29 projects into the cavity where it is bent back and attached to the outer conductor to form the probe 28. The outer conductor is held secure by coupler 30. Coupler 30 is fitted into a longitudinal slot 3| in outer conductor 21 of the cavity and is free to slide in order to adjust the position of the probe. The probe is placed at a point in the line where the desired harmonic-voltage signal is at a maximum. The probe feeds'the load connected to output terminal 33 through a high pass filter 32 which attenuates the fundamental frequency component and passes the harmonic frequency component.

A coaxial filter of the -typedescribed ingthe oopending patent application, entitledElectrical Apparatus, by Paul I. Richards, Serial Number 638,897, filed January 3, 1945, now abandoned, may be used. The center conductorof 'tliefilter, according to the application referred to, fcom prises a plurality of short sections of conductor {4- separated by thin pieces of dielectricmaterial 35. The innerconductor may be separated from the outer conductor by adielectric material.

The cavity effectively constitutes two sections of coaxial line having different characteristic impedancesand coacting inseries. Th characteristic impedance of a coaxial line isrelated to the ratio of the inside diameter of the outer conductor and the outside diameter of th -inner conductor. Thetwo coaxial lines coacting in series is equivalent to-alength, 9a (at the-fundamental frequency), ofa coaxial line having a characteristic impedance Za, and-terminated by a shortcircuited iengtmcb (at the fundamental frequency), of a coaxial line having acharacteristic im- :pedance equal to 'Zb, as showninFig. 2.

The lengths of the coaxial line sections may be adjusted by'ineans' of the rods attached to the 1-plungers and extending to the outside. When the line lengths are adjusted properly, cavity 28 is'resona'nt'at the fundamental" frequency of oscillation, and'simultaneously resonant at a desired harmonic frequency. For the cavity to be *resonant at the fundamental frequency of oscillation, the input impedance of the two sections of-coaxial line 'coacting inseries should be sub- :stantially infinite. This will occur when Equa- "tion 1, below,- i satisfied:

'"where 'm a factor defined by"tl'ie"rati'o Zia/Z1."

The electron"beain in thereflex tube will contain harmonic frequency components, and if the cavity is simultaneously "anti rsonant at this *harnionic' rrequency,harmonic"power will be detheir trigonometric identities gives:

Solving Equations 1 and 4 simultaneously gives: Ctn c i+ (-3m ''1)-' 'C'tn 0a+m =0 (5) The required 9a corresponding to any m may be computed, and 0b subsequently Y determined from Equations 1 or 2.

sigtn ca will bepositive and real only if MEI/3,

4 For the critical case when m=1/3, the required line lengths of 0s. and 0b are equal.

Power at a higher frequency than could normally be extracted from a klystron oscillator may be taken from the harmonic oscillator embodying the principles of this invention. When extractin harmonic power from the oscillator described, herein, the fundamental frequency of oscillation is -iniiependentof the: load imposed by the extraction means. The oscillator possesses excellent amplitude regulation, since loading at the harmonic frequency does not affect the 'bunchingaction of the klystron. In tuning the oscillator by the 'means presented herein, a rel- :atively-=broad-range of oscillating frequencies is possible. By -choosing a different harmonic frequency and substituting a corresponding high -pass'filterftl ie' range may be extended even far- -'-ther.-

While there has been described hereinabove what -is-at present considered .to be a preferred embodiment of this invention, it will be-- obvious to those skilled i-n-the artthat various changes and modifications may be made therein :wi-thout departing from th spirit and scope of the inven- -tion.

'Whatis claimed is:

l. A reflex klystronoscillator for high frequency operation comprising a cavity'resonator including a first coaxiallinehaving afirst-characteristic impedance and a second coaxial line coupled across one end of said firstline and having a second characteristic impedance, means coupled to both said lines tuning said cavity rescnator to a given frequency and to a harmonic frequency thereof,-the inner andouterbonductors of said first coaxial linebeing separated from one another by a .gapatthe' end of saidfirst line remote from the end coupled to said second line, said conductors of *said" first coaxial line being provided with a I pair'of apertures adi acent said gap, a source of electrons 'rnounted adjacent one "of said apertures for projecting electrons across saidgap; electron reflecting means mounted adjacent the other or said ap'ertures forreflecting electrons ba'ck acrosssaid -gap in "an interval of time to 1 excite "said 'resonator to oscillate at I a fundamental frequency equal to said gii/en'frequency, and "output cou'pli-ng means positioned in a region ofsaidresonator'whereenergy "of'said harmonic frequency-isa maxi-mum and energy of said given frequency is substantially lessthan quency operation comprising t a cavity resonator including a first eeaxial line having a' first ratio of inner-to-outer conductor diameters -and-a secondcoaxial line coupled in series across one end of said first line, and having a second ratio of inner-to-outer conductor diameters; a pair-of separately movable tuning-means one in each ofsaid lines for independently tuning said-lines-sothat the combination of saidlinesis resonant=at a givenfrequency and ate. harmonic frequency thereof, the inner and outer conductors of said first coaxialline being separatedfrom one another by a gap at-the end of said-first line remote from'the end coupled to said second-linesaid conductors of said firstline-being provided with apertures-adjacent said gap, a source-of electrons mounted adjacent one of said apertures for-projecting electrons across said gap, electron reflecting means mountedadjacent the other of said apertures for reflecting electrons back across said gap in an interval of time to excite said resonator to oscillate at a fundamental frequency equal to said given frequency, and movable output coupling means positioned in a region of said resonator where energy of said harmonic frequency is a maximum and energy of said given frequency is substantially less than that of said harmonic frequency for providing output energy of said harmonic frequency.

WILLIAM H. I-IUGGINS.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date Chevigny et al June 25, 1946 Whinnery July 16,1946 Morton Oct. 15, 1946 Fisk Nov. 19, 1946 Bailey Feb. 18, 1947 Morton Feb. 24, 1948 

